1. Field of the Invention
The present invention relates to a rocking fulcrum member and, more particularly, to a crisscross-spring-type rocking fulcrum member used in a lever-type detector or the like.
2. Description of the Related Art
In lever-type detectors or the like, a finger arm having a contactor attached to its tip is supported on a rocking fulcrum so as to be able to seesaw. The detector detects the amount of movement of the finger arm when the contactor is in contact with a work.
Examples of rocking fulcrum members used in such detectors are an elastic fulcrum such as shown in FIG. 7C, an L-shaped spring fulcrum such as shown in FIG. 7B, a bearing (not shown) and crisscross spring fulcrums such as shown in FIG. 7A. Elastic fulcrums are capable of operating with accuracy but can be used only in a case where the measurement range is narrow because they have only restricted swing angles.
L-shaped spring fulcrums are low-priced and are being widely used but have a drawback in that the fulcrum center is shifted with a swinging movement and cannot be suitably used as a precise fulcrum member. Bearing fulcrums can have any swing angle but need periodical replacement because their accuracy is reduced due to wear.
Crisscross spring fulcrums include those formed by disposing two plate springs so that the plate springs cross each other as shown on the left-hand side of FIG. 7A, and those integrally formed by being cut by wire cutting as shown on the right-hand side of FIG. 7A. The latter have sufficient rigidity and high accuracy during repeated use and can therefore be suitably used as a precise fulcrum.
A crisscross spring fulcrum such as shown on the left-hand side of FIG. 7A is fixed by screwing opposite ends of the two plate springs to members or by welding the opposite ends to the members. A method of die-casting a crisscross spring base member and embedding the opposite ends of the two plate springs in the crisscross spring base member at the time of casting is also used (see, for example, WO 98/20297 pamphlet).
A crisscross spring fulcrum having two plate springs welded to grooves in a cylindrical housing has also been proposed (see, for example, U.S. Pat. No. 3,807,029).
In assembly of the above-described crisscross spring fulcrum member fixed by screwing opposite ends of the two plate springs to members has problems that a considerably long time is required for assembly and variations in spring characteristic occur due to assembly errors. The crisscross spring fulcrum having two plate springs embedded in a crisscross spring base member by die casting as described in WO 98/20297 pamphlet and the crisscross spring fulcrum having two plate springs fixed to a base member by welding as described in U.S. Pat. No. 3,807,029 have a problem that a considerably long time is required for fabricating and the assembly and manufacturing costs are high and another problem that the plate springs are heated at a high temperature at the time of welding or die casting to degrade the spring characteristic.
The crisscross spring fulcrum integrally formed by cutting using wire cutting electrodischarge machining also has a problem that a considerably long time is required for fabricating and the manufacturing cost is high and another problem that the characteristic of the spring degrades with time due to microcracks caused by machining.